1. Field of the Invention
The present invention relates to a circuit and a method for controlling a timing of intermittent reception in radio equipment, and more particularly to a circuit and a method for controlling a timing of intermittent reception in radio equipment, which establish synchronism with a radio signal by receiving a synchronizing signal.
2. Description of the Related Art
Conventional radio equipment performs intermittent reception of a radio signal for the purpose of improving the battery saving efficiency. In the intermittent reception, the radio equipment controls to turn on a radio section and amplifies the radio signal for demodulation only when necessary information is included in the radio signal. On the other hand, when the radio signal includes no necessary information, the radio equipment controls to turn off the radio section.
As the radio equipment of this kind, for example, there has been known a portable radio terminal disclosed in Japanese patent laid-open application heisei 4-355524.
The radio equipment of this type performs intermittent reception at a timing such that only the radio signal including necessary information is received but the radio signal having no necessary information is not received. The radio terminal detects whether reception of the radio signal is enabled or not at the timing for receiving the radio signal. If reception of the radio signal is enabled for example, electrical field strength of a received signal is higher than predetermined strength, the radio terminal receives the radio signal. On the other hand, if reception of the radio signal is disabled, the radio terminal stops receiving the radio signal for a predetermined interval of time even at the timing for receiving the radio signal.
However, this radio terminal cannot receive the radio signal until a predetermined time lapses even if reception of the radio signal is again enabled in a period during which reception of the radio signal is stopped.
In particular, if this radio terminal is applied to the radio equipment which establishes synchronism with the radio signal by receiving a synchronizing signal that is repeatedly transmitted in a predetermined interval of time, reception of the synchronizing signal is delayed, resulting in a delay in establishment of synchronism with the radio signal. The radio equipment, therefore, cannot detect the information included in the radio signal until synchronism with the radio signal is established. Specifically, in a radio selective-calling receiver, since it is impossible to receive a call signal representing a call number coincident with its own call number, the radio selective-calling receiver can not carry out call annunciation.
Conventionally, in order to suppress the delay in reception of the synchronizing signal, the radio section is subjected to ON/OFF control for a predetermined time in the radio selective-calling receiver of this kind when the synchronizing signal is yet to be received. The ON/OFF control for the radio section, namely, the intermittent reception of the radio signal is called "synchro-establishment mode" and is previously set in the radio selective-calling receiver. Further, the radio selective-calling receiver controls to turn on and/or off the radio section so that only the radio signal including information which is required after reception of the synchronizing signal, namely a batch to which the radio selective-calling receiver belongs is amplified and demodulated. The ON/OFF control for the radio section, i.e., the intermittent reception of the radio signal is called "a batch reception mode" and distinguished from the synchro-establishment mode.
When a power supply is turned on, the radio selective-calling receiver performs intermittent reception of the radio signal in accordance with the predetermined synchro-establishment mode. Upon receiving the synchronizing signal obtained from the radio signal, the receiver carries out intermittent reception of the radio signal in accordance with the batch reception mode, and amplifies and demodulates only the batch to which the receiver belongs. If the call signal representing the call number coincident with its own call number is detected from this batch, the receiver performs call annunication to inform that an user is being called.
In this receiver, however, if an ON time during which the radio section is turned on in the synchro-establishment mode is set to be shorter in order to improve the battery saving efficiency, reception of the synchronizing signal is delayed. Thus, even if the call signal representing the call number coincident with its own call number is transmitted, this call signal cannot be received. Further, on the other hand, the ON time for the radio section in the synchro-establishment mode is set to be longer in order to avoid the delay in reception of the synchronizing signal, the battery saving efficiency is disadvantageously lowered.